I am already trying daily meditation and pomodoro technique for specific tasks.
2.Less news: stop watching tv and read less news. These make your brain process less information and reduce the cognitive overloads.
3.Single goal: decide what you want to do or what skill you want to achieve. Do not try to have multi-goal or multi-tasking while you are focusing. In general, you want to have zero distraction so no phone, youtube, music, email.
If you feel tired after 3-4 hours, do something else to relax your brain til you feel ready for the next session. Do not take it too serious and enjoy the process instead. It's getting better everytime so let it be and just have a good day!.
Its something I found myself doing less and less over the past 5 years and in 2019 made a conscious effort to change that.
Find a topic you are interested in and start reading more. Avoid short-form writings such as tweets, or stuff like that. If you dont have a lot of free time, start with reading articles of Medium.
Reading books are obviously better. It also helped me improve my focus and memory because you rarely finish a book in a single sitting, so you start getting used to remember what you read yesterday and get back into that context.
I'd recommend setting aside at least 30 minutes each day and forming that habit.
Basically, I write down a task (or a few smaller tasks) to tackle during a dedicated 1 hr. In this hour I can do nothing else.
I've found that I am forced into some kind of flow, and am forced to confront the discomfort that can come from actually focus on things. It's not hard to be uncomfortable for an hour a day.
I don't really know many others that do exactly this, but this has helped me (Also, I have ADHD and focus can be an issue for me).
Also knocking something out early in the day can create momentum and stop inertia.
Practicing a physical and skill-based activity implying many simultaneous urgent inputs tremendously enhances my focus and attention span. Most martial arts are adequate.